On an AR-15 receiver this is true. There are two modifications that need to be made to install the full-auto parts.

Not with the old ones like my SP1, this is incorrect. All I need is the drop in parts no modifications required, it's like this from the factory and it's not a machinegun. But it also means if I acquire the parts and if they are anywhere near in close proximity, like in the same building or property, then I do have a machinegun.

I did some looking and it looks like I was ill-informed and must recant